Organic EL elements employing organic substances are thought to have promising use as an inexpensive, large-area, full-color display element of the solid luminescence type, and many organic EL elements are being developed. In general, an organic EL element is constituted of a luminescent layer and a pair of facing electrodes between which the luminescent layer is interposed. When an electric field is applied to both electrodes, electrons are injected from the cathode and holes are injected from the anode. The electrons recombine with the holes in the luminescent layer and the energy level returns from the conduction band to the valence band, upon which energy is emitted as light. This phenomenon is luminescence.
Conventional organic EL elements have had problems of high driving voltage, low luminance, low luminescent efficiency, and considerable property deterioration. Recently, an organic EL element having a thin layer containing an organic compound which has such a high fluorescent quantum efficiency that it luminesces at a voltage as low as 10 V or below was reported (see Applied Physics Letters, Vol.51, p.913, 1987), and attention is now focused thereon. In this technique, a metal chelate complex, a fluorescent band layer, and an amine compound are used in a hole-injecting layer to obtain high-luminance green luminescence, and the luminance reaches several thousands of candelas per m.sup.2 at a DC voltage of 6 to 7 V.
However, from the standpoint of practical use in a full-color display as an illuminant, the three primary colors or white color should be emitted. Since the above prior art element employs a complex of 8-quinolinol with aluminum (Alq), the luminescence thereof is green. An element doped with a fluorescent dye has been reported as an improvement of the above element (see Journal of Applied Physics, Vol.65, p.3610, 1989). In this improvement, 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran (DCM) is used as a dopant to obtain red luminescence. However, the above improved element has problems of low durability, etc., and is hence unable to be put to practical use. Although various EL elements which likewise employ a fluorescent material as a dopant and hence emit lights having longer wavelengths than green have been developed, all these EL elements still have an insufficient luminance and have the serious problem that the stability thereof in repetitions of use is poor.
On the other hand, the organic EL elements which have attained a high luminance are those having a layer of an organic substance formed by vacuum vapor deposition. Although element production using a coating technique is desirable from the standpoints of the simplification of production process, processability, increase in element area, etc., the elements produced using any conventional coating technique are inferior in luminance and luminescent efficiency to the elements produced using vacuum vapor deposition. Thus, an important subject has been to heighten luminance and luminescent efficiency.